1. Field of the Invention
This invention relates generally to footwear and, more specifically without limitation, to an insole insert for footwear.
2. Description of the Related Art
Although children are usually born with normal arches, as a child begins to walk and body weight is applied to his feet as they bear against a supporting surface, his foot structure necessarily reacts by tending to flatten out under the weight-generated forces applied to the soles of his feet. If the child were walking only on natural supporting surfaces, e.g., the ground, the normal age for the child to be able to stand without the need of external support for his feet is generally considered to be approximately eight years of age. For purposes of improved appearance, convenience, endurance, etc., however, man-made products are generally applied to those supporting surfaces. Unfortunately, such "improved" surfaces tend to be detrimental to the human musculoskeletal structures, especially during the developmental stages when the child's foot structure is "soft" and incompletely formed. Due to such negative environmental influences on the human foot structure, shoes which provide proper support and shock attenuation should be worn for protection and prevention of structural injury.
As disclosed in U.S. Pat. No. 4,272,899, issued Jun. 16, 1981 to Jeffrey S. Brooks, the disclosures and teachings of which are incorporated herein by reference, a contoured insole structure may be provided in children's shoes to reduce abnormal stress from the heel to the metatarsals by properly supporting and stabilizing the feet during development thereof. By so doing, the associated stresses placed upon the medial column of the foot is also reduced, distributing the body weight more evenly on the sole of the foot.
More specifically, when walking or running, the lateral (outside) portion of the heel is generally the first part of the foot to strike the ground, with the foot then pivoting on the heel to bring the lateral part of the forefoot into a position whereat it bears against an underlying surface. At that point, the foot resides in a supinated (inclined upwardly from the lateral to the medial side of the foot). The foot then pronates until all of the metatarsal heads are in the horizontal plane (flat to the supporting surface) and the heel ideally is oriented perpendicularly to the underlying surface. The foot is then in a neutral position with the subtalar joint neither pronated nor supinated. The bone structural alignment should be firmly supported when the foot assumes such neutral position in order to prevent the ligaments, muscles and tendons of the foot from becoming over-stressed.
Various skeletal characteristics of the feet that are pertinent to proper foot support include the first, second, third, fourth and fifth metatarsal heads, indicated in phantom at M1 through M5 in FIG. 1; first, second, third, fourth and fifth metatarsal necks associated with the respective metatarsal heads M1-M5, indicated in phantom at N1 through N5; first, second, third, fourth and fifth proximal phalanges spaced distally from the respective metatarsal heads M1-M5, indicated in phantom at P1 through P5; and first, second, third, fourth and fifth metatarsal phalangeal joints spaced between the respective metatarsal heads M1-M5 and proximal phalanges P1-P5, indicated at J1 through J5 in FIG. 1. Further, various muscles and tendons characteristically interact to stabilize the foot during the sequence of progressive movements normally experienced in a walking or running gait in preparation for movement from the neutral position to a propulsive phase of the gait cycle, sometimes referred to as "toe-off" or "push-off".
Flexion of the first metatarsal phalangeal joint (i.e., the great toe joint) is normally approximately fifteen degrees to the associated metatarsal in a dorsiflexed position when standing, and increases between sixty-five and ninety degrees, depending on the available motion and the activity required by the joint just prior to lifting off the underlying supporting surface. The relationship among the foot bones is such that the first metatarsal phalangeal joint and the two small bones there beneath, the tibial sesamoid and the fibular sesamoid, should be displaced downwardly ("plantarflex") in order for the toe to function appropriately.
Thus, the progressive phases of gait are heel strike, when the heel hits the ground; distance, when stability of the arch is an essential necessity; and propulsive phase, as the heel lifts off the ground and the body weight shifts onto the ball of the foot. During the transition from the neutral position through toe off, it is preferable that the second and third metatarsals be firmly supported, and that the first metatarsal head plantarflex (move downward) relative the second and third metatarsal heads. The toes also should generally be firmly supported during toe-off so that they remain straight, and thus stronger, promoting a "pillar effect" by the phalanges.
To provide additional insight into some of the mechanisms of the human feet, it is known that the lower limbs of the human embryo begin to rotate internally ninety degrees from an external position at the pelvic girdle at approximately the eighth week of fetal development. At the twelfth week of development, the feet begin to dorsiflex, and around the sixteenth week of development, the completely inverted feet begin to event, all of which are part of the complex preparation of the lower extremity for upright, bi-pedal weight-bearing posture and locomotion. A child's feet and legs have sometimes been described as a loose bag of bones and cartilage floating in a mass of soft tissue until about age six. As a result, foot posture is a rapidly changing proposition for children under the age of six years. The true structure of a child's foot is not developed until approximately seven or eight years of age when development of the sustentaculum tali is generally complete. Further, eighty to ninety percent of the child's adult foot size is developed by the age of ten, with complete development occurring by approximately age 14-16 years in human females and age 15-17 years in human males.
When infants begin to bear weight, their feet begin to pronate excessively because their feet are not yet ready, without deformation, to be placed on an unnatural surface, such as a hard flat surface. As a result, if uncorrected, repeated weight-generated forces may cause these early weight-bearing feet to permanently deform (excessive pronation). Thus, such early-age, weight-bearing feet should preferably be maintained in proper postural alignment by providing a more natural environment therefor, such as a better supporting interface between the feet and the underlying supporting surfaces, thereby allowing the feet to develop as normally as possible during their postnatal development.
Therefore, as soon as the child begins to bear weight on his feet, usually around six to seven months of age, treatment to neutralize excessive pronation should be instituted. The user's feet should be placed in their individually most efficient position to function properly and to reduce excessive strain not only on the feet but also on the lower body structure supported by the feet. In an ideal foot posture situation for minimal stress, the position in which the feet as weight-bearing organs would normally realize greatest efficiency (including an optimal ratio of supination and pronation) is one in which the subtalar joint is approximately forty-two degrees from the transverse plane, approximately sixteen degrees from the saggital plane, and approximately forty-eight degrees from the frontal plane, sometimes referred to as the neutral position hereinbefore mentioned. In the neutral position, the leg and calcaneus are perpendicular to the weight bearing surface, and the knee joint, ankle joint and forefoot, including the plane of the metatarsal heads, are substantially parallel to the subtalar joint and to the walking surface.
A fully developed human foot can generally be described as having one of three basic types: normal, low arch ("flat foot"), or high arch. From an anatomical standpoint, normal and flat feet are capable of being functionally controlled by the same basic shoe control mechanism, while a high-arch foot is structurally different and may require a different supporting environment. For example, the amount of adduction ("pigeon-toedness") of the front part of a normal or flat foot in relation to the heel area of the foot is typically slight, while the amount of adduction in a high-arch foot is generally much greater. Further, the movement of a normal or flat foot during running is also substantially different from that of a high-arch foot. If proper support and stabilization is not properly implemented during their early formative development, fully developed feet may be more susceptible to, and be more prone to suffer from, various maladies, including the following:
(a) tearing of the plantar fascia tissues which connect the heel to the ball of the foot and support the arch of the foot, sometimes referred to as "plantar fascial tears" or "plantar fasciitis", which generally arise from stressful upward pulls on the calcaneus ("heel bone") and strain of the intrinsic or interior foot muscles, and is generally realized as heel pain; PA1 (b) excessive stress between adjacent metatarsals, sometimes referred to as "metatarsal stress fractures", generally arising from improper support of the talonavicular joint ("arch") and instability of the first ray ("great toe joint"); PA1 (c) irritation of the tissue associated with a small bone beneath the great toe joint, sometimes referred to as "tibial sesamoiditis", generally arising from inappropriate support of the talonavicular joint and/or inappropriate weight distribution between the various metatarsal phalangeal joints; PA1 (d) excessive bony growth on the top of the foot, sometimes referred to as "saddle joint deformity", generally arising from improper movement of the first metatarsal and realized in the form of degenerative arthritis; PA1 (e) inflammation and/or separation of tissue from the tibia, sometimes referred to as "shin splint", generally arising from improper articulation of the talonavicular joint between the ankle bone and the key supporting bone of the foot and generally realized as fatigue of the muscles in the front and back of the leg; and PA1 (f) bruising in the bottom center of the heel generally arising from disproportionally greater weight-generated forces applied thereto.
Such maladies should be given due consideration, both in youth and in adults, as the human foot may start to breakdown as a result of degenerative disease by the age of thirty-five years.
In view of the foregoing, it should be obvious that certain parts of the feet are generally subjected to higher stresses during standing, running and walking, and that other parts of the feet require different degrees of support for maximum biomechanical efficiency, particularly since high impact forces to the foot are generally transferred to other skeletal structures, such as the shins, knees, and lower back region.
Control of the user's foot must begin in the heel and proceed to the arch, including providing stability of the forefoot in order for the foot to function properly through the normal phases of gait. Various devices have been developed in attempts to provide needed support and stabilization for a user's feet. A frequent problem with most of such devices, however, is getting the devices to not only properly fit the user's feet but, in the case of insole inserts, to also fit the user's shoes while properly supporting and stabilizing the user's feet.
Thus, what is needed is a device, when placed into footwear, provides an appropriate amount of support and shock attenuation for different regions of the foot to thereby provide a proper environment that promotes a balanced foot position for healthy postural and skeletal structural development thus allowing the parts of the foot to function in a way which provides maximum efficiency, to prepare the body for stresses normally subjected thereto, and to protect those parts of the foot which are subjected to high impact forces.